1. Field of the Invention
The present invention relates to a release agent for use on a releasing sheet of an adhesive product, such as an adhesive tape, an adhesive sheet or an adhesive fastening product, for use in a variety of fields exemplified by the medical, office, construction, painting and packaging fields.
2. Discussion of the Background
A releasing sheet, which is endowed with releasability by applying a variety of release agents to the surface of a paper or plastic film base member, has been called a "releasing paper" or a "separator" and has been widely used in adhesive products. The releasing characteristic is mainly provided by a process comprising the steps of applying an organic solvent solution containing a release silicone to the surface of a base, and either drying the solution, heat curing it or adding a hardening agent to a crosslink silicone resin in order to fix it to the surface of the base.
Recently, due to the desire for a water-based emulsion or a solventless releasing silicone in order to overcome the problems of air pollution, fire hazards, maintaining worker sanitation and energy conservation, the quantity of this type of silicone being used increases year by year. However, in the case of the solventless silicone release agent, the crosslinking density must be raised because in order to minimize viscosity the molecular weight of the silicone is extremely small. Moreover, from an equipment standpoint there are difficulties in obtaining thin and uniform coatings, and accordingly there are problems with coating precision.
On the other hand, silicone emulsion type release agents are very widely used particulary in Europe and America. However, they suffer from a multiplicity of disadvantages such as the undesirable penetration of the paper surface due to inferior film forming characteristics thereof. Therefore, various improvements are necessary in order to achieve satisfactory characteristics and in order to reduce costs.
As the separators must have a wide range of peel force from small to large to adapt to various applications, the peel resistance value of pure silicone contained in the conventional release agent in which the tapes must be stacked at the time of application, is too small even if the separator is applied in a very small quantity. In order to adequately control the peel resistance value, a heavy release-controlling agent comprising units of SiO.sub.2 and (CH.sub.3) SiO.sub.1/2, or units of CH.sub.2 =CH(CH.sub.3).sub.2 SiO.sub.1/2 is used to adjust the value. However, there arises a problem in that the stability of the peel force becomes poor, and in that the agent is shifted to the surface of the adhesive agent, causing the adhesive force and tack to deteriorate.
An object of the present invention is to provide a release agent for a separator for use in an adhesive product, and more particularly to provide a release agent capable of keeping the working space clean at the time of manufacturing the separator and overcoming air pollution occurring due to volatilization and dispersion into the air.
Moreover, another object of the present invention is to provide a release agent capable of overcoming the difficulty in controlling the peel resistance value, deterioration of the stability of the peel force caused by the peel force controlling agent and deterioration of the adhesive force occurring due to the shift to the adhesive layer, which are problems encountered with the conventional pure silicone resin release agent.
Furthermore, another object of the present invention is to provide a low-cost release agent with which a recyclable releasing sheet can be manufactured without necessitating a polyethylene laminating process, a barrier coat using polyvinyl alcohol or the like to fill up the surface as required in the case of the conventional organic solvent type silicone release agent.